1. Technical Field
The present invention relates to a handover technique for maintaining communication when moving from one network to another network of different type during the communication in an interworking system between networks of different types such as mobile communication network such as W-CDMA and a wireless LAN.
2. Background Art
Engineers are working to develop a system that allows mobile phones capable of communicating in a wide area to interwork with a public wireless LAN service which enables fast data communication in a small area to complement each other. For example, a service is being contemplated that uses a terminal capable of accessing both mobile phone network and wireless local area network (WLAN) in such a system. This service uses a mobile communication network which covers a wide area around a base station to maintain a connection while the mobile phone is moving fast whereas it uses a wireless LAN to provide broadband access while the mobile phone is moving slowly or stays in one place.
For the interworking system, the 3GPP (3rd Generation Partnership Project) has standardized an architecture that implements a scenario in which a mobile terminal accesses the packet service of a mobile communication network through a WLAN. TS (Technical Specification) 22.234 of the 3GPP describes the requirements of such systems, TS 23.234 describes the architecture, and TS 33.234 describes the authentication method. Japanese Patent Application Laid-Open No. 2000-349829 describes a method in which handover of a packet call is performed between mobile phone networks by using a home agent 2613. The following is a description of an exemplary handover processing method performed when a mobile terminal that has access to both of a mobile communication network and a wireless LAN moves from a coverage area of the mobile communication to the wireless LAN while the terminal is performing packet access.
FIG. 26 shows a block diagram of an interworking system built in accordance with a conventional art. A mobile terminal 2601 in FIG. 26 has packet access means for both of a mobile communication network and a wireless LAN. The terminal 2601 represents UE (User Equipment) in the 3GPP specifications. A first base station 2602a and a second base station 2602b mutually convert a radio signal sent from the terminal 2601 to a wired signal and transfers the signal. The base stations represent Node B in the 3GPP specifications. The first base station 2602a covers cell M1 and the second base station 2602b covers cell M2.
A first WLAN access network 2603a and the second WLAN access network 2603b are packet-switched networks using a protocol such as IP (Internet Protocol) and include access points that provides connection to the mobile terminal 2601. The first WLAN access network 2603a covers cell L1 and the second WLAN access network 2603b covers cell L2. Both networks are correctively referred to as the WLAN access network 2603. The WLAN network 2603 converts a radio signal on a wireless LAN to a packet signal for a wired network. On the WLAN access network 2603, a DNS server performs address assignment. The WLAN access network 2603 represents WLAN AN (Access Network) in the 3GPP specifications.
A radio network controller 2604 is connected to base stations 2602 (also referred to as the first base station 2602a and the second base station 2602b) through IP and performs wireless terminal control and transfers control data and user data. The radio network controller 2604 is RNC (Radio Network Controller) in the 3GPP specifications. Advantageous effects of the present invention can be achieved in ATM connection with base stations 2602 as well.
A first WLAN gateway 2605a and a second WLAN gateway 2605b are connected with the first WLAN access network 2603a and the second WLAN access network 2603b, respectively, and transmit control data and user data for a wireless LAN to and from their respective WLAN access networks 2603. The first WLAN gateway 2605a and the second WLAN gateway 2605b represent WAG (Wireless Access Gateway) in the 3GPP specifications. Both are collectively called the WLAN gateway 2605. The WLAN gateways represent the wireless network controller in the attached claims.
A packet controller 2606 is connected to the radio network controller 2604, controls packet transmission within the mobile communication network and manages the status of mobile terminals 2601 that relates to packet transmission. It is assumed here that the packet controller 2606 uses IP to connect to the radio network controller 2604. The packet controller 2606 represents SGSN (Serving GPRS Support Node) in the 3GPP specifications.
A mobile network packet gateway 2607 is connected with the WLAN access networks 2603 through IP and relays packet data from the mobile communication network to the Internet. The mobile network packet gateway 2607 represents GGSN (Gateway GPRS Support Node) in the 3GPP specifications. One mobile network packet gateway 2607 is provided for each APN (Access Point Name) that is a domain of the mobile terminal 2601.
A packet data gateway 2608 is connected with the mobile network packet gateway 2607 and the WLAN gateways 2605 and relays data from these gateways to a public packet-switched network 2612. Like the mobile packet gateway 2607, the packet data gateway 2608 supports APN. It is assumed here that one packet data gateway 2608 is connected with multiple WLAN gateways 2605.
An authentication gateway 2609 is connected to the WLAN gateways 2605 and receives authentication data from the mobile terminal 2601 through the WLAN gateway 2605 when the mobile terminal 2601 enters the area covered by the wireless LAN. The authentication gateway 2609 represents AAA Proxy in the 3GPP specifications.
An authentication server 2610 is connected to the authentication gateway 2609 and receives authentication data from the mobile terminal 2601 through the authentication gateway 2609. The authentication server 2610 represents AAA Server in the 3GPP specifications.
A user information storing section 2611 is connected with the packet controller 2606, the mobile network packet gateway 2607, and the authentication server 2610 and stores information about services provided by the operator of the mobile communication network or wireless LAN to a user under a contract between the operator and the user. The public packet-switched network 2612 is a network made available to the public. The Internet is one of the public packet-switched network 2612.
A home agent 2613 relays data transmission from the mobile terminal 2601 and redirects data transmission in accordance with the location to which the mobile terminal 2601 moves. The home agent 2613 also manages the location of the mobile terminal 2601 by using mobile IP and registers the positioning of the mobile terminal 2601. A correspondent node 2614 is a node with which the mobile terminal 2601 performs packet communication. Examples of the correspondent node 2614 include servers on the Internet.
The mobile communication network and the wireless LAN that interwork with each other in the system will be defined as follows. The term “mobile communication network” refers to a network including mobile network packet gateways 2607, packet controllers 2606, radio network controllers 2604, and base stations 2602. The term “wireless LAN” refers to a network consisting of packet data gateways 2608, WLAN gateways 2605, and WLAN access networks 2603.
FIG. 27 shows components of a wireless LAN and stacks of protocols handled by the components. The mobile terminal 2601 has a remote IP layer 2701 for communicating with a correspondent node 2614 and a transport IP layer 2703 for performing IP communication over an access network of the wireless LAN. Different IP addresses for these layers are assigned to the terminal 2601, which are called the remote IP address and the local IP address.
Packets in the remote IP layer 2701 are relayed by the packet data gateway 2608 that is the entrance to the public packet-switched network 2612. A tunnel 2702 is provided between the mobile terminal 2601 and the packet data gateway 2608 through which packets at the remote IP layer 2701 are transmitted. The functions of the tunnel include the function of encapsulating packets, the function of compressing the header or payload of packets, and an encryption function. The terminal 2601 and the packet data gateway 2608 hold information about settings of the functions such as encapsulation, compression, and encryption schemes and connection setup information such as an access point name and a telephone number for each tunnel.
The transport IP layer 2703 is terminated at each node. Packets from the mobile terminal 2601 are terminated at a WLAN access network 2603. L1 (physical layer) and L2 (data link layer) are not particularly specified in this example.
The following is a description of a method for switching to communication over a wireless LAN when a terminal 2601 enters an area covered by the wireless LAN while communicating with a correspondent node 2614 over a mobile communication network in the system described above.
The mobile terminal 2601 performs IP packet communication as follows. First, user IP packets travel from the mobile terminal 2601 to the correspondent node 2614 via nodes of the mobile communication network and a home agent 2613. A remote IP address of user terminal is assigned by a mobile network packet gateway 2607 that routes remote IP addresses. The home agent 2613 manages a set of a home IP address, which is an address on the home network of the mobile terminal 2601, and a care-of address, which is an address of the mobile terminal 2601 that is used in the network to which the current position of the mobile terminal 2601 belongs (visited network). The home agent 2613 encapsulates the home IP address of the mobile terminal 2601 that is output from the correspondent node 2601, and transfers it to the care-of address.
IP packets from the mobile terminal 2601 are encapsulated and transferred, like packets transmitted in the reverse direction. If the correspondent node 2614 supports a Binding Update procedure, the procedure may be used to directly transmit IP packets to the mobile terminal 2601 and the correspondent node 2614, instead of using encapsulation.
On the mobile communication network, an IP tunnel is provided for each link between nodes and IP packets are encapsulated and then transferred. GTP (GPRS Tunneling Protocol) is used in communication between the mobile network packet gateway 2607 and the packet transmission controller 2606 and communication between the packet transmission controller 2606 and the radio network controller 2604.
The radio network controller 2604 converts IP packets to logical channel packets or transport channel packets as appropriate and then transferred to a base station 2602a by using IP transport. The base station 2602a converts them to W-CDMA physical channel packets and communicates with the terminal 2601.
When the mobile terminal 2601 enters an area covered by a wireless LAN while performing packet communication, the following process is performed. First, when the mobile terminal 2601 enters the wireless LAN area at 2801 in FIG. 28, the mobile terminal 2601 detects the radio field of the wireless LAN. It is assumed here that the wireless LAN is compliant with IEEE 802.11a/b/g. In the local connection process 2802, the first WLAN access network 2603a assigns a local IP address to the mobile terminal 2601.
Then, in the authentication process 2803, the terminal 2601 requests the user information storing section 2611 to authenticates the mobile terminal 2601 for making packet access through the WLAN. In the authentication, EAP (PPP Extensible Authentication Protocol) used by a first WLAN gateway 2605a, an authentication gateway 2609 (not shown in FIG. 28), and an authentication server 2610. If the authentication server 2610 does not have information about the user required for authentication, the authentication server 2610 obtains the information from the user information storing section 2611.
After completion of the authentication 2803, the mobile terminal 2601 queries DNS in the wireless LAN IP address acquisition process 2804. In response to this, the first WLAN access network 2603a returns a set of remote IP addresses and FQDNs of all networks that the mobile terminal can use and packet data gateways 2608 associated with them.
At a tunnel creation request 2805, the mobile terminal 2601 selects a packet data gateway 2608 from the IP addresses obtained in the IP address acquisition process 2804 and provides a request for creation of an IP tunnel using the set of remote IP addresses and FQDN to the packet data gateway 2608. In the authentication completion confirming process 2806, the packet data gateway 2608 communicates the authentication server 2610 via the authentication gateway 2609 to check to determine that the mobile terminal has been authenticated.
Then, in the policy exchange 2807, the packet data gateway 2608 and the first WLAN gateway 2603a exchange a packet transmission policy. The policy to use is determined by the packet data gateway 2608 and the first WLAN gateway 2603a applies the transmission policy provided from the packet data gateway 2608.
After the policy exchange, in the tunnel creation process 2808, the mobile terminal 2601 and the packet data gateway 2608 exchange tunnel attributes and a tunnel is created between them. The packet data gateway 2608 assigns a remote IP address to the mobile terminal 2601, which will be used as the IP address of the mobile terminal 2601 on the public packet-switched network 2612.
After the tunnel is created, the mobile terminal 2601 registers (remote IP registration 2809) the remote IP address in the home agent 2613. After the remote IP address is registered, the home agent 2613 changes the destination of packets from the correspondent node 2614 to the new remote IP address.
After a connection 2810 on the wireless LAN is established in this way, the mobile terminal 2601 disconnects the connection with the mobile communication network.
The interworking system between a mobile communication network and a wireless LAN as described above has a problem that the system requires much time to move across networks that use different access techniques because both authentication process and connection process must use equipment of a core network.
To solve the problem, an article entitled “Seamless handoff scheme using positional information in mobile IP network”, Institute of Electronics, Information and Communication Engineers technical report RCS2002-209, pp. 13-18, proposes a method for reducing switching time involved in handover. This scheme is an improved version of mobile IP, in which the GPS (Global Positioning System) is used to manage the positioning of a mobile terminal 2601 and the mobile terminal 2601 predicts the next cell to move to on the basis of the management data. Authentication and connection processes required for handover to the predicted cell are performed beforehand using a cell with which the mobile terminal can communicate at the time, thereby reducing the switching time required for the mobile terminal to move to the predicted cell. The method disclosed in the article predicts the next cell to move to by using GPS data, on the mobile terminal 2601, the IP address and position of the mobile terminal 2601, thereby simplifying connection setup.
Japanese Patent Application Laid-Open No. 2004-254278 discloses a method in which handover is performed when a mobile terminal moves between a UMTS area and a WLAN area in a system in which a WLAN access point is connected to a UMTS (Universal Mobile Telecommunications System), which is a type of W-CDMA.
In the method disclosed in Japanese Patent Application Laid-Open No. 2004-254278, a wireless LAN AP 2903, which is an access point of a wireless LAN, is connected with a packet controller 2906 through a WLAN IWF (Inter-Working Function) 2905, which is a functional element for interconnecting them, as shown in FIG. 29.
The wireless LAN IWF 2905 and the packet controller 2906 are interconnected through an Iu-ps interface. According to the GPRS specifications, when a packet connection is established on a mobile communication network, a primary GPRS context and a secondary GPRS context containing information concerning the packet connection are created. In the secondary GPRS context, connection information such as IP addresses and QoS are stored. The method disclosed in Japanese Patent Application Laid-Open No. 2004-254278 activates the secondary GPRS context concerning the wireless LAN in association with an ongoing packet connection session and changes the secondary GPRS context in accordance with the area in which the mobile terminal 2901 is located, thereby enabling the mobile terminal 2901 to switch between the mobile communication network and the wireless LAN.
For example, when a mobile terminal 2901 that has already established packet connection with a mobile communication network in cell M1 enters cell L1 that is an area of a wireless LAN, the following process is performed. The mobile terminal 2901 first starts establishing connection to a wireless LAN AP 2903. The mobile terminal then attempts to obtain an IP address on the wireless LAN. However, the mobile terminal 2901 cannot obtain a new IP address because the mobile terminal 2901 has a connection that has already established over the mobile communication network. Therefore, the mobile terminal 2901 uses the IP address it already has. It should be noted that QoS can be changed. Thus, parameters are set and a secondary GPRS context for the wireless LAN is added to a mobile communication packet gateway in addition to the secondary GPRS context for the mobile communication network that is already used. In this way, a secondary GPRS context containing QoS and other information, which vary from network to network, is created for each terminal and an appropriate secondary GPRS context is used for the area in which the terminal 2901 is located to accomplish handover.